A typical Complementary Metal Oxide Semiconductor (CMOS) image sensor has an image sensing portion that includes a photodiode for collecting charge in response to incident light and a transfer gate for transferring charge from the photodiode to a charge-to-voltage conversion mechanism, such as a floating diffusion. Usually, the sensing portion is fabricated within the same material layer and with similar processes as the control circuitry for the image sensor. In an effort to increase the number of pixels provided in an image sensor, pixel size has been decreasing.
However, as the pixel size shrinks, the illuminated area of the photodetector is also typically reduced, in turn decreasing the captured signal level and degrading performance.
Thus, a need exists for an improved image sensor structure.